Scientists have developed silken implants that actually conform to the surface of the brain. Researchers demonstrated that the ultra-thin, flexible implants could record brain activity more faithfully than thicker implants embedded with similar electronics.
When it comes to recording brain activity, the simplest devices currently available are made up of needle-like electrodes that penetrate deep into the brain. One major drawback is that these electrodes can damage the tissue they are trying to evaluate.
Some researchers have access to more sophisticated equipment called “micro-electrode arrays,” which consist of dozens of semi-flexible wire electrodes fixed to a silicon grid. While the microelectrode arrays may be safer, their rigid configuration prevents them from conforming to the brain’s shape, resulting in less accurate readings.
Researchers at the University of Pennsylvania’s School of Medicine in Philadelphia examined the limitations of current brain recording devices and developed the ultra-thin, silk-based arrays that can hug the brain like shrink wrap. A study of their new device was recently published in Nature Materials.
"The focus of our study was to make ultra-thin arrays that conform to the complex shape of the brain, and limit the amount of tissue damage and inflammation," said Brian Litt, M.D., an author on the study and an associate professor of neurology at University of Pennsylvania, in a press release.
To make and test the silk-based implants, Dr. Litt collaborated with scientists at the University of Illinois in Urbana-Champaign and at Tufts University, outside Boston. The flexible electronics were invented by John Rogers, Ph.D., a professor of materials science and engineering at the University of Illinois. The tissue-compatible silk was engineered by David Kaplan, Ph.D., and Fiorenzo Omenetto, Ph.D., professors of biomedical engineering at Tufts. Dr. Litt then used the electronics and silk technology to design the implants, which were fabricated at the University of Illinois.
The implants contain metal electrodes that are 500 microns thick—5 times the thickness of a human hair. The study has shown that the absence of sharp electrodes and rigid surfaces can improve safety and contribute to significantly less damage to brain tissue.
Aside from its flexibility, silk was chosen as the base material because it is durable enough to undergo patterning of thin metal traces for electrodes and other electronics. It can also be engineered to avoid inflammatory reactions, and to dissolve at controlled time points from almost immediately after implantation to years later. The electrode arrays can be printed onto layers of polyamide plastic and silk, which can then be positioned on the brain.
The ability of the new implants to mold to the brain's surface also means that if the organ moves—since the brain can sometimes shift in the skull—the implant could move along with it and still maintain an accurate reading.
By spreading across the brain, the implants also have the potential to capture the activity of large networks of brain cells, according to Dr. Litt.
"[These implants] could provide a platform for a range of devices with applications in epilepsy, spinal cord injuries, and other neurological disorders," said Walter Koroshetz, M.D., deputy director of the National Institute of Neurological Disorders and Stroke (NINDS), in a press release.
In people with epilepsy, the arrays could be used to detect when seizures first begin, and deliver pulses to shut the seizures down. In people with spinal cord injuries, the technology has promise for reading complex signals in the brain that direct movement and routing those signals to healthy muscles or prosthetic devices.
Scientists hope to use this technology to design implants that are more densely packed with electrodes to achieve higher resolution recordings. One researcher explained that it might also be possible to compress the silk-based implants and deliver them to the brain through a catheter, in forms that are instrumented with a range of high-performance, active electronic components.
The flexible material could have applications to other parts of the body as well. The team described a flexible silicon device for recording from the heart and detecting an abnormal heartbeat.
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